From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7EF0CC3ABC9 for ; Thu, 15 May 2025 08:55:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=W4rTId6THWoa765N3ANlRit5ailmKTqHblTIleVnKKU=; b=cSZyHwNd6nP56byIqTZjVD7VUu rriHT9GEPHENARrfi71MyVRnUXRUG/VyFlT3dKnvD1UprNHc+nMY8oyInohCsOrGJPGWUomT4wac4 llB5fxwFiKSQBK5cZxoneseDgvtvc4y6E9i0jQTxaUZZZmqB1LaDLiHajV0Pkx413xZl6F30YbGBI aaZdkEy42UhxLsm1R9eMTAyNtKP58BNrrQoPOdP2AIFjOsRBI3JU2O0L/eUJWQidlQdvIhzooRhd5 nqGJBJZ9rdmtE94Pl4BeXWIb/79aUNN3N/O/6uLP0g8HHjUjf6zGpB46f6defrYHd8+Wha2DnhQ7e 5ANqPXOw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uFUNI-000000003cQ-2huY; Thu, 15 May 2025 08:55:32 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uFU8U-000000001OC-2gYw for linux-arm-kernel@lists.infradead.org; Thu, 15 May 2025 08:40:15 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C79D014BF; Thu, 15 May 2025 01:40:01 -0700 (PDT) Received: from [10.162.40.26] (K4MQJ0H1H2.blr.arm.com [10.162.40.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2E50B3F673; Thu, 15 May 2025 01:40:09 -0700 (PDT) Message-ID: <73a67d06-b497-40a2-8cb2-3b80c6ba59d1@arm.com> Date: Thu, 15 May 2025 14:10:07 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: Check pxd_leaf() instead of !pxd_table() while tearing down page tables To: David Hildenbrand , catalin.marinas@arm.com, will@kernel.org Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, mark.rutland@arm.com, yang@os.amperecomputing.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org References: <20250515063450.86629-1-dev.jain@arm.com> <332ecda7-14c4-4dc3-aeff-26801b74ca04@redhat.com> <4904d02f-6595-4230-a321-23327596e085@arm.com> <6fe7848c-485e-4639-b65c-200ed6abe119@redhat.com> Content-Language: en-US From: Dev Jain In-Reply-To: <6fe7848c-485e-4639-b65c-200ed6abe119@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250515_014014_722834_FA19A4B0 X-CRM114-Status: GOOD ( 16.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 15/05/25 2:06 pm, David Hildenbrand wrote: > On 15.05.25 10:22, Dev Jain wrote: >> >> >> On 15/05/25 1:43 pm, David Hildenbrand wrote: >>> On 15.05.25 08:34, Dev Jain wrote: >>>> Commit 9c006972c3fe removes the pxd_present() checks because the caller >>>> checks pxd_present(). But, in case of vmap_try_huge_pud(), the caller >>>> only >>>> checks pud_present(); pud_free_pmd_page() recurses on each pmd through >>>> pmd_free_pte_page(), wherein the pmd may be none. >>> The commit states: "The core code already has a check for pXd_none()", >>> so I assume that assumption was not true in all cases? >>> >>> Should that one problematic caller then check for pmd_none() instead? >> >>   From what I could gather of Will's commit message, my interpretation is >> that the concerned callers are vmap_try_huge_pud and vmap_try_huge_pmd. >> These individually check for pxd_present(): >> >> if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr)) >>     return 0; >> >> The problem is that vmap_try_huge_pud will also iterate on pte entries. >> So if the pud is present, then pud_free_pmd_page -> pmd_free_pte_page >> may encounter a none pmd and trigger a WARN. > > Yeah, pud_free_pmd_page()->pmd_free_pte_page() looks shaky. > > I assume we should either have an explicit pmd_none() check in > pud_free_pmd_page() before calling pmd_free_pte_page(), or one in > pmd_free_pte_page(). > > With your patch, we'd be calling pte_free_kernel() on a NULL pointer, > which sounds wrong -- unless I am missing something important. > >> >>> >>> If you were able to trigger this WARN, it's always a good idea to >>> include the splat in the commit. >> >> I wasn't able to, it is just an observation from code inspection. > > That better be included in the patch description :) I did, actually. My bad for not putting in spaces, I notice now that the description looks horrible to the eye :) >